Health care providers, researchers, and medical device makers have invested considerable resources in efforts to effectively improve the vision of or provide vision to those with little or no vision capabilities. Various types of retinal disease can be the cause of complete or near blindness, such as age-related macular degeneration and retinitis pigmentosa. Each is a degenerative disease that causes severe degradation of the outer retina. Macular degeneration causes loss of central vision, making reading impossible, while retinitis pigmentosa initially causes gradual loss of peripheral vision, followed by loss of central vision resulting in total blindness.
The retina is a light-sensitive layer at the back of the eye that includes photosensitive cells called rods and cones. The optic nerve is a collection of nerve fibers that carry electric signals generated from light stimulation of the rods and cones to the brain for vision processing. In each disease above, the rods and cones at the back of the retina degenerate. As the degeneration progresses, the retina becomes increasingly insensitive to light. This ultimately causes blindness. Importantly, the optic nerve is not affected as significantly as the outer retina—the pathway to the brain remains available and viable for communicating electrical signals to the brain for vision processing.
In the conditions described above, proper stimulation of the remnant retina could improve or return sight to the vision impaired or blind patient. Toward that end, retinal prosthesis have been developed that can be implanted in the eye as a means of stimulating the rods and cones from the surface of the retina. In fact, U.S. Pat. No. 5,597,381, entitled Methods of Epi-Retinal Implantation, describes approaches for implanting a retinal prosthesis over the retina through an incision in the sclera. As described in the patent, implantation of the prosthesis allows electrical stimulation of the retinal neurons to convey at least the outlines of a visual scene transmitted to the prosthesis as by an infrared laser, radio frequency source or other wireless techniques from outside the eye. While the retinal prosthesis does not enable substantially restored vision, it offers relative improvement and the implantation techniques may be useful for makers of improved retinal prosthesis.
To date, the most common retinal prosthesis use flexible electrodes developed for stimulation of peripheral nerves and retina. These use polymers such as polyimide, poly dimethyl siloxane, and parylene as substrates for embedding arrays used to electrically stimulate the retina. Generally, greater coverage of the retina by electrodes in the retinal prosthesis enables more complete stimulation of the retina, and therefore better vision. With prior typical retinal electrode arrays or prosthesis the size of scleral incision must be bigger than the width of the prosthesis to be able to insert the prosthesis into the eye. However, a big scleral incision can distort the shape of the eye and may be associated with more surgical complications; as a result, current retinal prosthesis are small in size, which has the disadvantage of covering only a small area of the retina.
U.S. Pat. No. 6,368,349, entitled Inflatable Neural Prosthesis, discloses an approach for implanting a relatively large retinal prosthesis through a relatively small opening. The prosthesis disclosed in this patent includes a foldable substrate and at least one electronic component supported by the substrate, with at least one micro-channel disposed within the substrate for providing a fluid for inflating (i.e., unfolding) the prosthesis after being inserted through the incision in the sclera. However, too much fluid pressure during inflation could cause the prosthesis to be damaged, which could in turn cause damage to the eye. Additionally, the required micro-channel adds a level of complexity and cost to the prosthesis, and consumes area that could have been otherwise used for the stimulation electrodes. Thus, inflatable retinal prosthesis have certain drawbacks. For example, like other retinal prosthesis, they cannot easily conform to the curvature of the eye and if the array is big, some parts of it may be far away from the retina, while the other parts may exert pressure on the retina and cause retinal damage.